How many games do you participate in?
I run one game...which was never my intention, but after three co-GMs utterly dropped the ball each time the GM needed to take time away from the game, I offered to take the job (I'd been part of the game from its inception). The GM's been gone for a few years, but I promised I'd see it through to the end, so...I limp along as best I can. *grin*
I'm in three games...one is very active and usually has multiple posts per day, one typically has multiple posts per week, and one is very casual and usually ends up updating once every other week. There are two other games that I have characters in, but nothing has been posted in either of them in months, and there was another game I was in that ran in fits and starts, but it's actually run its course.
So, at one point, I was running one, playing in six...only rarely were they all active at the same time, but when they were, it was a LOT to stay on top of. With the three I'm in now that are running, plus the one I run, I'm tempted to look for another game or two...but remembering how chaotic it was when they were all active at the same time keeps me from doing it.
How many is too many? That's a personal thing...how much computer access do you have? How much leisure time do you have? How adept are you at juggling multiple lines of thought? It's unlikely that any two people have identical answers to those questions, so there's not really a formula for it. On top of that, different types of games require different levels of attention. Three games that update once a week demand less focus than a single game that updates daily. So, really, you're the only one who can decide whether you have too many games or room for one more.